Photoconductive pickup tube field mesh support



May 23, I. T. SALD I PHOTOCONDUCTIVE PICKUP TUBE FIELD MESH SUPPORT Filed April 2, 1965 22 23 F|G.l.

INVENTOR: I IDEAL T. SALDI,

v HIS ATTORNEY.

United States Patent 3,321,655 PHQTOCONDUCTIVE PICKUP TUBE FIELD MESH SUPPORT Ideal T. Saldi, Manlius, N.Y., assignor to General Electric Company, a corporation of New York Filed Apr. 2, 1965, Ser. No. 445,015 7 Claims. (Cl. 313-65) ABSTRACT OF THE DISCLOSURE A pickup or camera tube having improved means for supporting a decelerating field mesh electrode closely adjacent a target electrode, said means comprising a plurality of insulative spacers members secured to the said means and to another electrode of the tube.

This invention relates to a photoconductive camera or pickup tube having a field mesh electrode supported adjacent the photoconductive target, and more particularly, to an improved method for mounting a decelerating field mesh electrode closely adjacent the target electrode and electrically isolated therefrom.

Photoconductive camera or pickup tubes known as Vidicon camera tubes, generally comprise an envelope structure having electron gun means in one end thereof, and a target electrode of a transparent photoconductive coating at the other end. The electron gun directs a controlled beam of electrons to the photoconductive target. It has been found desirable in many instances to provide a fine mesh type electrode adjacent the photoconductive target to decelerate the electron beam and thereby control certain characteristics of the pickup tube. It has also been found desirable, in a number of applications, to provide the mentioned field mesh electrode not only in close proximately to the photoconductive target but also to be electrically insulated therefrom. The electrical insulation provides means to control or vary the electrical potential of the field mesh and thereby, as a primary purpose, minimize or suppress secondary emission of the mesh for a higher resolution pickup tube.

Ordinarily the structure of a photoconductive pickup or Vidicon tube is such that the electron gun assembly usually includes component parts such as a cylindrical focusing electrode which projects from the electron gun end of the pickup tube to a position adjacent the photoconductive target. Accordingly, it has been the usual and convenient practice to mount or support the field mesh electrode on the end of such afocusing electrode. There are, however, certain problems which must be considered in the mounting of these decelerating field mesh electrodes. More particularly, the mounting structure must be rather uncomplex to provide ease in assembling and disassembling. At the same time the mounting structure must be sufiiciently secure so that critical spacings between the field mesh electrode and the photoconductive target are maintained during operation of the tube. Furthermore, the materials of construction of the supporting assembly must also utilize materials which are compatible with photoconductive pickup tube use in that they do not contaminate the environment or provide 3,321,655 Patented May 23, 1967 foreign materials which interfere with the effective operation of the photoconductive surface.

Accordingly, it is an object of this invention to provide an improved mounting assembly for the decelerating field mesh in a photoconducitve pickup camera tube.

It is another object of this invention to provide improved electrical isolating supporting means for the decelerating field mesh of a photoconductive pickup camera tube.

It is yet another object of this invention to provide a more simplified structure for supporting and electrically insulating a field mesh electrode adjacent the photoconductive target electrode of a photoconductive pickup camera tube.

Briefly described, this invention in one of its preferred forms includes a plurality of electrically insulating glass bead members fixedly attached in equally spaced relationship about the periphery of the end of a cylindrical focusing electrode which is adjacent the photoconductive target of a pickup camera tube. A planar frame assembly which includes a field mesh electrode is thereafter concentrically positioned in engaging relationship with the mentioned glass beads and transversely to the focusing electrode so as to be electrically insulated and spaced from the focusing electrode. More particularly, in an operative embodiment of this invention three glass beads spaced apart peripherally of a cylindrical focusing electrode maintain a further cylindrical frame assembly including a transverse mesh electrode in electrically isolated and spaced relationship therefrom.

This invention will be better understood when taken in connection with the following description and the drawings in which FIG. 1 is a partial cross-sectional view of one preferred embodiment of this invention;

FIG. 2 is an end View of FIG. 1 taken on the line. 22, and

FIG. 3 is a cross-sectional and exploded view of a supporting head assembly of this invention.

Referring now to FIG. 1, there is illustrated one preferred embodiment of this invention as incorported within a well known photoconductive or Vidicon camera tube 10. Camera tube 10 comprises an evacuated envelope structure 11, usually in the form of a cylindrical glass wall, which contains the particular required camera tube elements. For example, the camera tube 10 includes an electron gun section 12 at one end thereof, having the necessary components operative to provide and control an electron beam therein. Tube 10 also includes a target section 13 spaced from the electron gun section and adapted to receive the mentioned electron beam. Target section 13 includes an optically transparent transverse face plate 14 hermetically sealed to envelope 11 by means of a suitable glass-to-glass seal 15. The inner surface of face plate 14 is employed to support a photoconductive target 16. Target 16 generally comprises a suitable coating of a photoconductive material applied to face plate 14 and positioned and adapted to be scanned by the electron beam from electron gun section 12 of tube 10. Suitable electrical control is exercised over this electron beam by means of a cylindrical focusing electrode 17 which extends concentrically from within the electron gun section 12 to a point in target section 13 adjacent target 16.

In order to decelerate the electrons in the electron beam which is scanning the target 16, a decelerating electrode 18 in the form of :a planar mesh or screen is positioned transversely between the end of control electrode 17 and target 16 and generally parallel with target 16. While there are various means by which mesh electrode 18 may be suitably supported in its operative and illustrated position, it is desirable that mesh 18 be electrically isolated from other components in tube 10. This isolation is necessary in order to provide a suitable potential to mesh electrode 18 which is different from other operating potentials of adjacent components, not only for the optimum deceleration of electrons but also for control of secondary emission of the mesh electrode, and stray electrons and ions. Additionally, it may also be desirable to provide means for changing or otherwise varying the potential of mesh electrode 18 for adjustment or during operation of the camera tube. While the target adjacent end 19 of the focus electrode 17 provides an expedient surface from which :to support mesh electrode 18, the supporting or mounting means should be of a simple nature whichfacilitates the assembly of the mount and related structure. At the same time the supporting means must provide a rigid structure capable of withstanding shock and vibration.

The mesh 18 supporting means of this invention includes a mesh frame support 20, a flanged member 21, a spacer shield 22, a support ring 23, and a plurality of insulating blocks or beads 24 which are suitably attached to the adjacent end of electrode 17 and support the recited components in electrically insulating relationship therefrom. As illustrated in FIG. 1, the spacer shield 22 engages both the internal periphery of envelope 11 and support ring 23 which is attached to beads 24. Therefore, shield 27 spaces end 19 of cylinder electrode 17 in concentric relationship within the tube structure.

The defined concentricity and positional interrelationship of the components are clearly illustrated in the end view of FIG. 2. In FIG. 2., mesh electrode 18 is shown as overlying annular flange member 21 and secured thereto by means of ring frame 20. Spacer shield 22 coextensively engages the inner periphery of envelope 11 while its inner or concentric aperture contains flange member 21. This combination provides a rigid structure to support end 19 of electrode 17, to maintain concentricity as well as parallelism of target and mesh electrode 18, and is sufliciently flexible to withstand severe shock and vibration.

Referring now to FIG. 3, there is illustrated in exploded view a more detailed interrelationship of the described component parts. In FIG. 3, a plurality of and preferably three bead members 24 are utilized in equally spaced relationship about the end 19 of control electrode 17. More particularly, beads 24 are of an electrically insulating material preferably of glass or other such ceramic and are attached to both the electrode 17 and support ring 21. As illustrated, one preferred form of attachment includes suitable tab members 25 which are fixed to support ring 21, for example by welding, in equidistant relationship about the periphery thereof. Other such tab members 25 are suitably fixed to end 19 of control electrode 17 in equally spaced relationship about the periphery thereof. The respective tab members 25 on ring 21 are oppositely positioned with respect to tab members 25 on the end 19 of control electrode 17. In assembly of ring 21 to control electrode 17, the parts are assembled in their operating relationship as illustrated, and glass beads 24 in a softened condition are pressed down over the upstanding arm members 26 on tabs 25. Upon cooling of the glass beads 24, support ring 21 will be maintained in rigid engagement with the glass beads 24 and in turn with control electrode 17. Accordingly, support ring 21 is electrically insulated from the control electrode 17. At the same time the concentricity of control ring 21 with electrode 17 is retained through the use of three heads 24 spaced apart about the periphery of control electrode 17. The connection between support ring 21 and control electrode 17 is an extremely rigid one being able to withstand severe shock without any electrical contact therebetween, and potential lateral and axial movement of support ring 21 is substantially eliminated.

The spacer shield 22 is generally an annular member whose cross section represents a generally U shape having the inner arm 27 of a length in excess of that of the outer arm 28. The inner arm 27 describes the inside diameter of the shield member 22 and is concentrically fitted within and engaging support ring 21 in a friction grip relationship. The outer arm 28 defining the outer periphery of spacer shield 22 is in a light frictional or close fitting engagement with the inner surface of envelope 11. Spacer shield 22 therefore operates not only to maintain the concentric relationship of the components in the target section of tube 10* but also acts as an effective barrier to any foreign material which may be dislodged or present within the tube 10 from coming into contact with target 16 when the tube is employed in a downward or vertical relationship.

Field mesh 18 usually comprises a fine mesh or woven metal wire screen for example copper with a mesh size of 60 or more and must be supported in a planar and taut condition. In order to support mesh electrode 18 in the defined manner, the periphery thereof is secured between a ring member 20 and flange member 21. Flange member 21 comprises a cylindrgzal section 28 and lateral flange 29. Mesh 18 is placed on flange 29 parallel thereto and covers the face of member 21. Thereafter, metal frame ring 20 is positioned concentrically on flange 29 and over the periphery of mesh 18. Ring member 20 is suitably joined to flange member 29 as for example by welding in order to maintain mesh 18 in a taut relationship over the face of member 21. As illustrated in FIG. 3, the mesh assembly 30 is then inserted into spacer shield 22 so that the axial extension 28 fits within the defined periphery of arm 27 in a friction gripping relationship thereto. The friction fit may be enhanced by the indentions 31 between the two surfaces. In order to ascertain the tightness of fit of axial extension 28 within the member 22, the inner arm 27 of member 22 may be provided with a plurality of equally spaced upstanding indentions or ridges 31 which tightly engage the axial extension 28.

The axial position or the distance of mesh electrode 18 from photoconductive target 16 is maintained in predetermined relationship by means of the component par-ts interfitting in abutting relationship. For example, flange 29 abuts shield 22 while shield 22 abuts support ring 21. The spacing between support ring 21 and cylinder is fixed by the beads 24. Thus the fitting or assembling of the parts provides the correct predetermined space between mesh 18 and target 16.

Electrical connection may be made to mesh electrode 18 by means of a suitable electrical conductor 32 (FIG. 1) which is supported by electrode 17 and which leads to one of the pin connections 33.

While this invention has been described with reference to particular and exemplary embodiments thereof, it is to be understood that numerous changes can be made by those skilled in the art without actually departing from the invention as disclosed, and it is intended that the appended claims include all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What is new and desired to be secured by Letters Patent of the United States is:

1. A photoconductive camera tube comprising in combination (a) an evacuated envelope,

(b) a photoconductive target in said envelope at one end thereof,

(0) an electron gun in said envelope spaced from said target and adapted to direct an electron beam toward said target,

(d) said electron gun including a control electrode extending to a point adjacent said target electrode,

(e) and a mesh screen electrode positioned transversely between said control electrode and said screen,

(f) said screen electrode being electrically insulated from and supported by said cylindrical control electrode,

(g) said supporting means including at least three electrically insulating ceramic bead elements fixedly attached to the periphery of said control electrode,

(h) a supporting cylindrical ring positioned concentrically with said control electrode and spaced therefrom,

(i) means fixedly attaching said ring to said electrically insulating beads,

(j) and an annular frame assembly containing said screen electrode concentrically positioned within said supporting ring and in concentric relationship thereto and releasably secured thereto.

2. A photoconductive camera tube comprising in combination (a) an evacuated envelope,

(b) a photoconductive target in said envelope at one end thereof,

(c) an electron gun in said envelope spaced from said target and adapted to direct an electron beam toward said target,

(d) said electron gun including a control electrode extending to a point adjacent said target electrode,

(e) and a mesh screen electrode positioned transversely between said control electrode and said screen,

(f) said screen electrode being electrically insulated from and supported by said cylindrical control electrode,

(g) said supporting means including at least three electrically insulating ceramic bead elements fixedly attached to the periphery of said control electrode,

(h) a supporting cylindrical ring positioned concentrically with said control electrode and spaced therefrom,

(i) means fixedly attaching said ring to said electrically insulating beads,

(j) an annular spacer shield means concentrically positioned in said envelope and engaging said envelope and said supporting ring to support the said cylindrical electrode and,

(k) an annular frame retaining a transverse mesh electrode thereon,

(l) and means securing said frame to said spacer shield.

3. A photoconductive pickup camera tube comprising in combination,

(a) an evacuated envelope,

(b) a photoconductive target in said envelope,

(c) an electron gun in said envelope spaced from said target and adapted to direct an electron beam toward said target,

(d) said electron gun having a cylindrical control electrode terminating adjacent said target,

(e) at least three electrical insulating glass bead support means fixedly attached to the end of said control electrode in equally spaced peripheral relationship thereon and projecting axially therefrom,

(f) a support ring positioned at the end of said control electrode and concentric therewith and axially spaced therefrom,

(g) means fixedly attaching said ring to said support beads for electrical insulation from said control electrode,

(h) envelope spacing means engaging said envelope and extending into said support ring to concentrically position and support said control electrode in said envelope,

(i) an annular frame assembly having a supported thereon, and

(j) means supporting said annular frame from within said spacer with said planar mesh transverse to the open end of said control electrode.

4. A photoconductive camera tube comprising in combination,

(a) an evacuated cylindrical envelope,

(b) a photoconductive target in said envelope at one end thereof,

(c) an electron gun in said envelope adjacent the other end thereof and adapted to direct an electron beam toward said photoconductive target,

(cl) a hollow cylindrical control electrode adjacent said electron gun and positioned concentrically within said envelope and extending to a point adjacent said photoconductive cathode,

(e) at least three equally spaced electrically insulating glass beads fixedly attached to the end of said control electrode adjacent said photoconductive electrode, and axially projecting therefrom,

(f) a metal support ring positioned concentrically with the open end of said control electrode and spaced therefrom and concentric therewith,

(g) means fixedly attaching said support ring within said electrically insulating beads,

(h) an annular imperforate spacer shield ring having a generally U-shaped cross section and positioned concentrically in said envelope so that the outer arm of said U-engages said envelope,

(i) the inner arm of said U cross section being positioned within and engaging the inner periphery of said support ring and in frictional engagement therewith,

(j) a cylindrical frame assembly having a planar mesh electrode supported transversely thereon,

(k) said frame assembly being slidably inserted within the inner arm of said annular spacer shield so that said frame assembly engages the inner surface of said inner arm of said spacer means.

5. A mounting structure for mounting field decelerating mesh electrodes in photoconductive pickup camera tubes comprising in combination,

(a) a hollow cylindrical electron beam focusing electrode adjacent the target of said tube,

(b) at least three projecting tab means fixedly attached to the outer periphery of said focusing electrode in equal spaced relationship,

(c) a support ring coaxial with and axially spaced from said focusing electrode,

(d) at least three projecting tab means fixedly attached to the outer periphery of said support ring in equal spaced relationship,

(e) the said tabs on said support ring and the said tabs on said focusing electrode being in opposite axial relationship,

(f) a glass bead member bridging and fixedly secured to opposite tab means,

(g) an annular spacer shield having a U cross section to define inner and outer cylindrical sections with the outer section engaging said envelope,

(h) the inner cylindrical section of said spacer shield being slidingly retained concentrically within and engaging said support ring,

(i) an annular frame having a planar mesh electrode transversely at one end and a projecting cylinder extension at the other end,

(j) said projecting cylindrical section being slidably retained concentrically within and engaging said inner cylindrical section of said spacer shield.

6. The invention as recited in claim 5 wherein a control electrode is in contact with said projecting cylindrical extension to provide a predetermined potential to said mesh electrode.

7. For use in a photoconductive camera pickup tube a planar mesh mounting for the decelerating field mesh electrode comprising,

(a) the combination of three engaging and interfitting metal cylinders,

(b) the first and outer of said cylinders comprising a support ring axially spaced from, concentric with, and electrically insulated from a tubular focusing electrode by insulating spacers,

(c) the second and intermediate cylinder fitting within said first cylinder comprising a spacer member in contact with the envelope of said tube and supporting said first cylinder in said envelope,

((1) the third and inner cylinder fitting within said second cylinder and comprising a flanged member supporting a transverse mesh electrode over the outer end thereof, and (e) an electrode in contact with said flange member.

References Cited by the Examiner UNITED STATES PATENTS 2,951,962 9/1960 Miller et al. 313269 X 3,202,857 8/1965 Antoniades 313269 X 3,202,861 2/1965 Spangler 313268 ROBERT SEGAL, Examiner.

JAMES W. LAWRENCE, Primary Examiner. 

7. FOR USE IN A PHOTOCONDUCTIVE CAMERA PICKUP TUBE A MOUNTING FOR THE DECELERATING FIELD MESH ELECTRODE COMPRISING, (A) THE COMBINATION OF THREE ENGAGING AND INTERFITTING METAL CYLINDERS, (B) THE FIRST AND OUTER OF SAID CYLINDERS COMPRISING A SUPPORT RING AXIALLY SPACED FROM, CONCENTRIC WITH, AND ELECTRICALLY INSULATED FROM A TUBULAR FOCUSING ELECTRODE BY INSULATING SPACERS, (C) THE SECOND AND INTERMEDIATE CYLINDER FITTING WITHIN SAID FIRST CYLINDER COMPRISING A SPACER MEMBER IN CONTACT WITH THE ENVELOPE OF SAID TUBE AND SUPPORTING SAID FIRST CYLINDER IN SAID ENVELOPE, (D) THE THIRD AND INNER CYLINDER FITTING WITHIN SAID SECOND CYLINDER AND COMPRISING A FLANGED MEMBER SUPPORTING A TRANSVERSE MESH ELECTRODE OVER THE OUTER END THEREOF, AND (E) AN ELECTRODE IN CONTACT WITH SAID FLANGE MEMBER. 